Every homeowner and electrician is familiar with the problem of determining which of several fuses or circuit breakers in a large array corresponds to an outlet or appliance in a separate room or in some other location out of sight. For example, assume that one wishes to know which circuit breaker controls the power to the outlet into which a bedroom lamp is plugged. Most people faced with this task are consigned to having to stand at the circuit breaker panel and use trial and error, and several trips back and forth to the outlet in question, in order to determine which circuit breaker controls the outlet.
U.S. Pat. No. 4,095,212 (Pruitt, Jun. 13, 1978) describes a remote electric state tester. With the Pruitt tester, the user plugs a transmitter unit into the outlet in question and then carries a receiver unit to the circuit breaker of fuse panel. As long as the units are working properly and there is electrical power being supplied through the outlet, the transmitter sends a continuous signal to the receiver, which in turn activates a steady indicator light as long as the receiver senses the signal. The user may remain at the circuit breaker or fuse panel, and when he disconnects the right circuit to cut off power to the outlet, the transmitter stps transmitting. If all is working well, the user will then know he has found the right circuit breaker or fuse because the indicator light will go out.
The Pruitt tester has several weaknesses, both in terms of reliability and of convenience. First, the transmitter described in the Pruitt patent requires separate pairs of input terminals for high- and low-voltage AC power from the tested outlet. When the test outlet has high-voltage AC, the user must manually switch the transmitter to the terminals which feed a transformer which is coupled to either an AC relay or to a DC relay which further requires the input power to be at least half-wave rectified and smoothed.
The user of the Pruitt device must consequently know or determine ahead of time whether the test current is in the correct "high" or "low" voltage range relative to the transmitter, and he must manually set the switch accordingly. The unit itself relies on standard electromechanical relays, and especially in a dusty, dirty, and occasionally damp construction or industrial environment such relays and/or their contacts may become soiled and useless.
An additional disadvantage of the Pruitt device is that the AC input circuit of the transmitter unit is electrically isolated from the actual RF transmission circuit, with the only connection being via a relay. Because of this, a separate battery must be provided in the transmitter unit to power the transmission circuit, and a separate test switch is needed to be able to test the strength of the battery. In other words, not only is the Pruitt transmitter not compact and light-weight enough to be convenient, the user must also make sure to have a sufficiently fresh battery in the unit, and to open and close the unit when the battery must be changed. This problem is all the more acute in the Pruitt receiver unit, which separates its reception circuitry from its indication circuitry, and which consequently requires separate batteries and check switches for each circuit. The Pruitt device as disclosed thus needs three separate batteries for proper operation.
Furthermore, the Pruitt transmitter unit is shown as being a floor unit connected to the test outlet by means of an electrical cord. Although necessary because of the weight of the ferrous components such as the transformer and relays, this means that the unit is not compact enough for the user to carry easily, for example in his or her pocket. The usefulness of the Pruitt tester is further reduced by the fact that no provision is made to adapt the tester to outlets which use different kinds of socket holes, for example, three-pronged as well as two-pronged, flat blades as in the U.S. as well as pins as in Europe, screw-in sockets as well as plug-in, etc.
The Pruitt device also includes a switch for testing the receiver's indicator light. By closing this switch, the indicator light is connected directly to the battery and, if whole, will light up. This feature allows the user to test the light, but it is inadequate. If the user is standing at the fuse box and the indicator light is shining, he will assume there is power at the test outlet. If, however, the relay which is also required in the receiver is not working properly, the indicator light may continue to shine even though the test outlet has been disconnected.
It is consequently the object of this invention to provide a remote circuit tester which is light-weight, compact, and easily adaptable to different test outlets and appliances.
Another object of the invention is to provide a remote circuit tester which automatically adjusts to the level of the input current, delivers robust and highly reliable performance and security, using non-mechanical components, and which needs at most only a single battery.